Many of monomers having reactive unsaturated bonds can produce polymers by performing a reaction under an appropriate condition by means of a catalyst for causing a chain reaction. Such monomers having unsaturated bonds can be typified, for example, by versatile monomers including vinyl compounds such as styrene, alkylstyrene, and alkoxystyrene. In addition, a wide variety of polymers each having a different property are synthesized by copolymerizing such vinyl compounds alone or copolymerizing these vinyl compounds with each other. When these polymers are industrially used, a homopolymer using one kind of monomer cannot satisfy diverse conditions that are required for a material. For this reason, a method of mixing heterogeneous polymers is employed. However, simple mixing of heterogeneous polymers yields separation of polymers that are not miscible with each other (referred to as macro phase separation), and thus a mixture of heterogeneous polymers does not exhibit characteristics of each polymer in many cases.
For solving the problems above, known is a block copolymer in which two or more polymer segments are chemically bonded to each other. In the mixture of heterogeneous polymers, phase separation occurs since polymers are not easily miscible with each other as described above. However, in the block polymer, the phase separation structure thereof has a size of nanometer (referred to as micro phase separation) since the polymer segments are chemically bonded to each other. For such reasons, characteristics of each polymer segment can be exhibited without inhibiting the characteristics of each polymer segment. Among the block copolymers, a (meth)acrylic block copolymer is being applied for various uses which require transparency or weather resistance.
Further, an acrylic resin molded article has exceptional transparency, but has a problem that it is hard and brittle. As a method of obtaining a transparent and pliable acrylic resin molded article, generally known is a method of adding core-shell-type rubber particles to an acrylic resin molded article. However, in the method, since rubber particles are produced by emulsion polymerization, the particle diameter of the rubber particles becomes 100 nm or more, and thus there is a problem that sufficient pliability cannot be achieved in an acrylic resin molded article added with these rubber particles.
For solving the problems above, known is an acrylic resin molded article obtained by using the above-described (meth)acrylic block copolymer in which two or more polymer segments are chemically bonded to each other. The phase separation structure of the (meth)acrylic block copolymer has micro phase separation since (meth)acrylic block copolymers are chemically bonded to each other. For this reason, characteristics of each polymer segment can be exhibited without inhibiting the characteristics of each polymer segment. Therefore, as compared to the method of adding core-shell-type rubber particles, it is expected to obtain an acrylic resin molded article having exceptional transparency and pliability.
As a method for producing a (meth)acrylic block copolymer, for example, the following method is proposed in Patent Document 1. Patent Document 1 describes a method in which a macromonomer, which is produced by using a cobalt chain transfer agent having a very high chain transfer constant, is used as a chain transfer agent, and then the macromonomer is copolymerized with another (meth)acrylic monomer in a solution to thereby obtain a (meth)acrylic block polymer. In Patent Document 1, the block copolymer is produced by a solution polymerization method or an emulsion polymerization method. In the method for producing a block copolymer by a solution polymerization method, the obtained block copolymer solution (hereinafter, referred to as the polymer solution) can be directly used for use as a coating material, but when the obtained polymer solution is used for an application other than a coating material, a recovery step of the polymer such as re-precipitation is required. Further, in the solution polymerization method, environmental load is large in terms of using a solvent in the recovery step. In addition, in an emulsion polymerization method, heat stability or transparency of a block copolymer to be obtained may be deteriorated due to a residual of an emulsifying agent in some cases.